1. Field
Apparatuses consistent with exemplary embodiments relate to a light amount adjusting device, and more particularly, to a light amount adjusting device having a compact structure and having optical performance improved by maintaining an aperture through which light passes in a hexagonal shape similar to a circular shape when adjusting the size of the aperture.
2. Description of the Related Art
In photographing apparatuses such as digital cameras, video cameras, or CCTVs, an image sensor receives light from an object and converts the light into an electric signal, and a light amount adjusting device such as an aperture stop adjusts the size of an aperture through which light is incident on the image sensor.
Photographing apparatuses such as surveillance cameras also include a light amount adjusting device configured to block the path of light for adjusting the amount of light and responsivity to light. If the depth of field is adjusted by varying the size of an opened area using a light amount adjusting device, a distant or close object may be clearly photographed.
Korean Patent Application Laid-open Publication No. 1993-0000979 discloses a light amount adjusting device of the related art. When the size of an aperture through which light passes is adjusted using the light amount adjusting device disclosed in the above-identified Publication, the shape of the aperture is irregularly varied, which may cause i) imbalanced variations in the amount of light, ii) occurrence of asymmetric diffraction or chromatic aberration at an image sensor, or iii) splitting or spreading of light. Particularly, when the size of an aperture of an aperture stop is maximally reduced, the aperture is shaped almost like a rhombus, causing failure in focusing and blurs in images. In addition, for example, when a scene including a very bright object such as a region in which light passes between leaves is photographed, the region is blurred and shaped like a rhombus which is similar to the aperture shape of an aperture stop, and thus unnatural images may be captured.
FIG. 23 is s schematic view illustrating an example of light amount adjusting devices of the related art.
The light amount adjusting device of the related art illustrated in FIG. 23 has a mechanism in which an aperture 511 is closed or opened using wings 520 and 530, each having a recess 521 and 531, respectively.
Although the aperture 511 for sending light to a photographing apparatus is designed to have a circular shape as a whole, as the light amount adjusting device is operated, a shape of a hole formed by the wings 520 and 530 of the light amount adjusting device does not match the shape of the aperture 511, and thus light may split or spread. That is, if the light amount adjusting device of the related art is used, partially unfocused images may be captured. In addition, because the aperture 511 of the light amount adjusting device is shaped like a rhombus relatively long in a horizontal or vertical direction, optical aberrations may be different in longitudinal and lateral directions. Therefore, the resolution of captured images may be imbalanced in the longitudinal and lateral directions, and the amount of light may differ in the longitudinal and lateral directions. That is, the quality of captured images may be low.
It has been attempted to vary the shape of the aperture of the light amount adjusting device to a polygonal shape similar to a circular shape. According to the attempt, however, the number of wings forming the aperture is increased, and the amount of movement of the wings is increased. Thus, it is difficult to manufacture light amount adjusting devices having a small size. For example, if a light amount adjusting device having a hexagonal aperture is designed using six wings, a relatively large motor is used to drive the six wings, and the number of components and the overall volume of the light amount adjusting device are increased.
The structure of a light amount adjusting device including three linear movement wings is disclosed in Japanese Patent Application Laid-open Publication No. 1998-301159 and Japanese Patent No. 5173979. According to the disclosed structure, the distances that the wings travel from maximally opened positions to closed positions are relatively long. Thus, the size of the light amount adjusting device is increased in width and length directions because the length of a rotary link driving the wings is increased to increase the amounts of movement of the wings. That is, it is difficult to reduce the size of the light amount adjusting device.
Japanese Patent No. 4735997 discloses the structure of a light amount adjusting device including six wings: two linear movement wings and four rotation wings. According to the disclosed structure, the light amount adjusting device may maintain a hexagonal aperture shape. However, because a disk member connected to the six wings using pins is placed in the light amount adjusting device to drive the six wings, the number of components, size, and thickness of the light amount adjusting device increase. In addition, due to friction between the disk member and the six wings, torque for driving the disk member and the six wings increases, and thus a large driving motor and a large decelerator are used.
Light amount adjusting devices of the related art having a polygonal aperture as described above have a relatively large volume and a relatively large number of components, and incur high manufacturing costs, and thus it is difficult to apply such light amount adjusting devices to apparatuses such as surveillance cameras or camcorders.